Shift control method for an automatic transmission

ABSTRACT

PCT No. PCT/JP96/01593 Sec. 371 Date Feb. 11, 1997 Sec. 102(e) Date Feb. 11, 1997 PCT Filed Jun. 12, 1996 PCT Pub. No. WO96/41978 PCT Pub. Date Dec. 27, 1996A shift control method for an automotive automatic transmission is provided, which reduces a shift shock particularly at the time of a skip down-shift, and shortens a required shifting time period. An electronic control unit of a shift control apparatus releases the engagement of a clutch of a subsidiary transmission mechanism and engages a one-way clutch so as to establish a gear position not used in the normal speed change when a shift command from the fifth shift position to the third shift position is issued, gradually decreasing a valve opening duty ratio of an electromagnetic valve associated with a brake of a main transmission mechanism from an initial value DHLi before this gear position is established, determines an average turbine rotation speed changing rate dDTAVE/dt from the detected turbine rotation speed (S203), and learning correction of the initial value DHLi is made if the changing rate deviates from a target range (S204-S208).

TECHNICAL FIELD

This invention relates to a shift control method for an automatictransmission, and more particularly, to a shift control method for anautomatic transmission which is capable of reducing a shift shock causedby a skip down-shift and shortening a time period required for shifting.

BACKGROUND ART

An automotive automatic transmission generally includes a transmissionmechanism having planetary gear units which include shift changeelements (hereinafter referred to as gears) such as sun gears andplanetary carriers and having hydraulic friction engaging elements suchas hydraulic wet-type multiple disk clutches and hydraulic band brakes(hereinafter referred to as clutches and brakes, respectively). In anautomatic transmission of this type, the gear connection is changed overby releasing one(s) of the friction engaging elements associated withshift change and by engaging the other friction engaging element(s)associated with shift change, to select those gears which contribute totorque transmission, to thereby establish a desired shift position.

In recent years, in order to improve the drivability of automobiles andreduce the fuel consumption, attempts have been made to further enhancethe degree of electronic control for automatic transmissions andincrease the number of shift positions or transmission stages. A typicalmulti-stage automatic transmission includes a main transmissionmechanism constructed by an existing transmission mechanism and asubsidiary transmission mechanism coupled in line, in respect of torquetransmission, with the main transmission mechanism. Those gears of thetwo transmission mechanisms which contribute to torque transmission arecombined in various manners, to thereby establish an arbitrary one of arequired number of shift positions, e.g., five forward shift positionsand one reverse shift position. For example, the gear connection in themain transmission mechanism is changed over to effect a shift changeoperation among the first, second and third shift positions, and thegear connection in the subsidiary transmission mechanism is changed overto effect a shift change operation between the third and fourth shiftpositions. Further, to carry out a shift change between the fourth andfifth shift positions, the gear connection in the main transmissionmechanism is changed over, with the gear engagement state (torquetransmission path) in the subsidiary transmission mechanism set so as tocorrespond to the fourth shift position. In other words, by use of thesubsidiary transmission mechanism, a switching is made between thelower-speed shift positions including the first through third shiftpositions and the higher-speed shift positions including the fourth andfifth shift positions.

In an electronic controlled automatic transmission, a shift mapdetermined as a function of vehicle speed and throttle valve openingdegree, as shown in FIG. 13, is generally used to select a shiftposition. From this map, an optimum shift position (target shiftposition) suitable to detected values of the vehicle speed and throttlevalve opening degree is selected. In the case of a kick-down at a rapidacceleration, the target shift position is generally determined by thethrottle valve opening degrees. That is, when the throttle valve openingdegree traverses the 5-4 shift line or 4-3 shift line shown in FIG. 13,a down-shift command is output. As a result, if the accelerator pedal isdepressed by the driver and the throttle valve opening degree θ reachesthe point B from the point A in FIG. 13, a down-shift is carried outfrom the fifth shift position to the fourth shift position. When thethrottle valve opening degree θ reaches the point C from the point A, aso-called skip down-shift from the fifth shift position to the thirdshift position is effected.

On an occasion that a direct down-shift from the fifth shift position tothe third shift position is effected in the aforementioned multi-stageautomatic transmission, that is, a skip down-shift is effected, it isnecessary to make the changeover of gear connection in both of the mainand subsidiary transmission mechanisms. However, to simultaneouslycontrol a plurality of transmission mechanisms, an advanced techniquesuch as the modern control theory must generally be used.

Further, in the automatic transmission, the shift control is generallyeffected based on the outputs of two rotation speed sensors respectivelyindicating the rotation speeds of the input and output shafts of thetransmission. However, the shift change condition in each of the mainand subsidiary transmission mechanisms cannot be detected based on theoutputs of the two sensors. Therefore, it is extremely difficult tosimultaneously control the shift change operations in both of thetransmission mechanisms based on the two sensor outputs. Provision ofadditional rotation speed sensors makes it possible to detect the shiftchange condition of each transmission mechanism, and, in turn, tosimultaneously control a plurality of transmission mechanisms. In thiscase, however, the cost rises.

Conventionally, therefore, in order to carry out a skip down-shift, thegear connection in the main transmission mechanism is first changedover, and then the changeover of gear connection is made in thesubsidiary transmission mechanism. For example, for the down-shift fromthe fifth shift position to the third shift position, a method has beenadopted in which the fourth shift position is temporarily establishedduring the downshift, so that the downshift is carried out by way of thefourth shift position. However, this type of shift control methodentails the following defects.

As is well known in the art, the release of a clutch or brake, which isa hydraulic friction engaging element, requires a predetermined periodof time corresponding to a response delay in oil pressure release.Therefore, even if a down-shift command for instructing a shifting tothe third shift position is issued immediately after the temporaryestablishment of the fourth shift position, the fourth shift position iskept established until the predetermined time period elapses because ofthe presence of the delay in oil pressure release. Further, to establishthe fourth shift position, it is necessary to make a time-consumingdetermination as to the synchronization of rotation speeds of the inputand output shafts of the transmission. According to the conventionalmethod in which a skip down-shift is made by effecting a one-stepdown-shift plural times, a shift shock occurs each time the one-stepdown-shift is effected and a period of time required for shiftingbecomes longer. Therefore, the ride qualities and shift response aredegraded.

DISCLOSURE OF THE INVENTION

An object of this invention is to provide a shift control method for anautomatic transmission, which is capable of alleviating a shift shockoccurring at the time of shifting, particularly at the time of a skipdown-shift, and capable of shortening a time period required forshifting.

The shift control method according to this invention is applied to anautomotive automatic transmission having a main transmission mechanismand a subsidiary transmission mechanism arranged in series with eachother in a power transmission system. Each transmission mechanism isconstructed so as to selectively establish plural gear positions. Theautomatic transmission is constructed so as to selectively establish thefirst and second shift positions by a combination of a gear positionestablished in the main transmission mechanism and a gear positionestablished in the subsidiary transmission mechanism.

The shift control method according to this invention comprises the stepsof starting a shift change operation for establishing a gear position,corresponding to the second shift position, in either one of the mainand subsidiary transmission mechanisms in response to a shift commandinstructing a shift from the first shift position to the second shiftposition; starting a shift change operation for establishing a gearposition, corresponding to the second shift position, in the othertransmission mechanism before the shift change operation in said one ofthe transmission mechanisms is completed; detecting an input shaftrotation speed of the automatic transmission; and learning-correcting avalue of a parameter governing the start of the shift change in theother transmission mechanism based on a changing rate of the input shaftrotation speed.

An advantage of this invention is that a smooth relation can be attainedbetween the shift change operation on the main transmission mechanismside and that on the subsidiary transmission mechanism side even in acase where the automatic transmission entails manufacturing variationsor deterioration with the lapse of time. As a result, a shift change(particularly, a skip down-shift) on the automatic transmission canstably be carried out smoothly within a short period of time, and ashift shock (particularly in the skip down-shift, a shift shockoccurring when the speed change on the one transmission mechanism iscompleted) can be reduced.

In this invention, preferably, the parameter value learning-correctingstep includes learning-correcting the parameter value based on achanging rate of the input shaft rotation speed observed during a timeperiod from a time the shift change operation in said one transmissionmechanism is completed to a time a predetermined period of time haselapsed since the start of the shift change operation in said onetransmission mechanism. More preferably, the parameter valuelearning-correcting step includes determining an average value ofchanging rates of the input shaft rotation speed and learning-correctingthe parameter value based on the average value.

According to these preferred embodiments, a determination as to whetheror not, immediately after the completion of the shift change operationon one of the main and subsidiary transmission mechanisms, the shiftchange operation on the other transmission mechanism is started properlycan be made exactly. Also, the learning correction of the parametervalue can be made so as to meet the result of the above determination.As a result, the shift change operation on the other transmissionmechanism can be started more properly once the learning correction hasbeen made, and therefore, a shift shock can be reduced.

In this invention, preferably, the parameter is an engagement force ofthat friction element which is released when the second shift positionis established. The step of starting the shift change operation in theother transmission mechanism includes decreasing the engagement force ofthe friction element. More preferably, the step of starting the shiftchange operation in the other transmission mechanism includes decreasingthe engagement force of the friction element to a preset value. Theparameter value learning-correcting step includes learning-correctingthe preset value based on the changing rate of the input shaft rotationspeed.

According to these preferred embodiments, it is possible to exactlydetermine whether or not that engagement force (preferably, the presetvalue of the engagement force) is proper which is observed when theshift change operation on said other transmission mechanism is startedimmediately after the completion of the shift change operation on saidone of the main and subsidiary transmission mechanisms. Also, thelearning correction of the value of engagement force (preferably, thepreset value of engagement force) can be made in a manner suitable tothe result of this determination. As a result, the shift changeoperation on the other transmission mechanism can be started properly,and a shift shock can be reduced.

Preferably, the shift control method according to this invention furthercomprises a step of detecting torque of the input shaft. The step oflearning-correcting the parameter value includes learning-correcting thevalue of the parameter for each of those regions which are divided inaccordance with the input shaft rotation speed or the input shafttorque.

According to this preferred embodiment, the learning correction of theparameter value can be made finely in accordance with a vehicleoperating condition. Therefore, once the learning correction has beenmade, the shift change operation on the other transmission mechanism canbe performed in a state more suitable for the vehicle operatingcondition at the start of the shift change, so that a shift shock can bereduced further.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a shift control apparatus forembodying a shift control method according to a first embodiment of thisinvention, together with an automatic transmission;

FIG. 2 is a skeleton diagram showing the gear train of an auxiliarytransmission shown in FIG. 1;

FIG. 3 is a flowchart showing a 5-3 shift control subroutine executed bythe shift control apparatus show FIG. 1;

FIG. 4 is a flowchart showing in detail a 5-4' shift control subroutineshown in FIG. 3;

FIG. 5 is a flowchart showing in detail a preceding control subroutineshown in FIG. 4;

FIG. 6 is a flowchart showing in detail a 4'-3 shift control subroutineshown in FIG. 3;

FIG. 7 is a graph showing a change in the turbine rotation speed withelapse of time during the 5-3 shift;

FIG. 8 is a graph showing a change with elapse of time in the valveopening duty ratio of an electromagnetic valve which is associated witha fourth clutch shown in FIG. 2 and serving as a releasing-side frictionengaging element in the 5-4' shifting process;

FIG. 9 is a graph showing a change with elapse of time in the valveopening duty ratio of an electromagnetic valve which is associated witha third brake shown in FIG. 2 and serving ass an engaging-side frictionengaging element in the 5-4' shifting process;

FIG. 10 is a graph showing a change in the valve opening duty ratio ofan electromagnetic valve which is associated with a first clutch shownin FIG. 2 and serving as an engaging-side friction engaging element inhe 4'-3 shifting process;

FIG. 11 is a graph showing a change in the valve opening duty ratio ofan electromagnetic valve associated with a second brake which serves asa releasing-side friction engaging element in the 4'-3 shifting process;

FIG. 12 is a graph showing, by way of example, a predetermined timeperiod T_(a) -turbine torque T_(TM) map referred to in the 5-3 shiftcontrol subroutine;

FIG. 13 is a diagram showing a shift map determined as a function ofvehicle speed and throttle valve opening degree;

FIG. 14 is a graph showing a change in the turbine rotation speed N_(T)with elapse of time which change is observed when the pressure of oilsupplied to the second brake immediately after the establishment of 4'thshift position is determined is too low;

FIG. 15 is a graph showing a change in the turbine rotation speed N_(T)with elapse of time observed when the pressure of oil supplied to thesecond brake is too high;

FIG. 16 is a graph showing a change in the turbine rotation speed N_(T)with elapse of time observed when the pressure of oil supplied to thesecond brake falls within proper range;

FIG. 17 is a flowchart of a learning-correction routine for a duty ratioD_(H) which is executed in parallel with the shift control routinesshown in FIGS. 3 to 6; and

FIG. 18 is a flowchart showing in detail a subroutine, shown in FIG. 17,for the calculation of an average changing rate of the turbine rotationspeed.

BEST MODE OF CARRYING OUT THE INVENTION

With reference to the accompanying drawings, a shift control apparatusfor an automotive automatic transmission will be described in detail towhich apparatus a shift control method according to one embodiment ofthis invention is applied.

Referring to FIG. 1, an automatic transmission 2, which is comprised ofa torque converter 3, an auxiliary transmission 4 and a hydrauliccontroller 5, is drivingly coupled with the crank shaft (not shown) ofan engine 1 to transmit an output torque of the engine 1 to drivingwheels (not shown) of a vehicle. In other words, the automatictransmission 2 forms part of a power transmission system of the vehicle.

The auxiliary transmission contains a plurality of sets of planetarygear units and hydraulic friction engaging elements such as hydraulicclutches and hydraulic brakes. The hydraulic controller 5 is formed witha hydraulic circuit, not shown, to which pressurized operating oil issupplied from a hydraulic pump (not shown) driven by the crank shaft ofthe engine 1. In the hydraulic circuit, a plurality of electromagneticvalves (not shown) duty-driven by an electronic control unit (ECU) 6 aredisposed. These electromagnetic valves are operated under the control ofthe ECU 6 to control the supply of oil to the hydraulic frictionengaging elements of the transmission 4 so as to establish a desired oneof a plurality of shift positions, for example, five forward shiftpositions and one reverse shift position, of the transmission 4.

The ECU 6 has an input/output device, memory devices (nonvolatile RAM,ROM or the like), a central processing unit (CPU), timer counters andthe like, which are not shown in the drawings. The ECU 6 has its inputside to which are connected a vehicle speed sensor 7 for detecting thetraveling speed V of the vehicle, an N_(T) sensor 8 (input shaftrotation speed detecting means) for detecting the turbine rotation speedN_(T) of the torque converter 3, that is, the rotation speed of thetransmission input shaft, a throttle sensor 9 for outputting a voltageV_(TH) indicating the throttle valve opening degree θ (engine load), anN_(O) sensor 8a or detecting the rotation speed N_(O) of thetransmission output shaft, and an N_(E) sensor 8b for detecting theengine rotation speed. The ECU 6 cooperates with the sensors 7, 8, 8a,8b and 9 and the hydraulic controller 5 to form a shift controlapparatus for carrying out the shift control method of this embodiment.In addition to the sensors 7 to 9, the ECU 6 is connected to varioussensors and switches such as an inhibitor switch for detecting theposition of the shift lever. Since these elements are not directlyrelated to this embodiment, they are not shown in the drawing.

Referring to FIG. 2, the auxiliary transmission 4 includes a maintransmission mechanism 10, and a subsidiary transmission mechanism 30coupled in line, from the viewpoint of engine torque transmission, withthe main transmission mechanism 10. The main transmission mechanism 10includes an input shaft 11 coupled to a turbine 3a of the torqueconverter 3 for rotation in unison therewith, and first and secondplanetary gear units 12 and 13 supported on the input shaft 11. Inputsides of first, second and third clutches 15, 17 and 19 are drivinglycoupled to the input shaft 11. The clutches 15, 17 and 19 each haveinput and output sides which are engaged with each other when operatingoil is supplied to an oil chamber (not shown) containing an engagingpiston of the clutch and the engagement between which is released whenthe operating oil is discharged from the oil chamber. The output sidesof the first, second and third clutches 15, 17 and 19 are respectivelycoupled to a sun gear 14 of the first planetary gear unit 12, a pinioncarrier 16 of the second planetary gear unit 13, and a sun gear 18 ofthe second planetary gear unit 13.

Therefore, the sun gear 14 and the input shaft 11 are drivingly coupledto each other when the first clutch 15 is engaged, the pinion carrier 16and the input shaft 11 are drivingly coupled to each other when thesecond clutch 17 is engaged, and the sun gear 18 and the input shaft 11are drivingly coupled to each other when the third clutch 19 is engaged.

In the main transmission mechanism 10, first and second brakes 22, 23each containing an engaging servo device (not shown) are mounted to acasing 20 of the transmission 4. The first brake 22 is designed to bebrought into an engaged state to fix an internal gear 21 of the firstplanetary gear unit 12 to be unrotatable, when operating oil is suppliedto a servo device of the first brake and to permit rotation of theinternal gear 21 when the operating oil is discharged from the servodevice. Likewise, the second brake 23 fixes the sun gear 18 of thesecond planetary gear unit 13 when operating oil is supplied thereto andpermits rotation of the sun gear 18 when the operating oil is dischargedtherefrom. The internal gear 21 of the first planetary gear unit 12 andthe pinion carrier 16 of the second planetary gear unit 13 are arrangedto rotate together, the pinion carrier 24 of the first planetary gearunit 12 and the internal gear 25 of the second planetary gear unit 13are arranged to rotate together, and the pinion carrier 24 is directlycoupled to the drive gear 26. Rotation of the input shaft 11 istransmitted to a driven gear 31 on the subsidiary transmission mechanism30 side via the planetary gear units 12, 13 and drive gear 26.

The subsidiary transmission mechanism 30 includes a counter shaft 32,and a third planetary gear unit 33 and a fourth clutch 36 which aresupported by the counter shaft 32. The input and output sides of thefourth clutch 36 are engaged when operating oil is supplied to an oilchamber (not shown) containing an engaging piston thereof, and theengagement of the input and output sides thereof is released when theoperating oil is discharged therefrom. The third planetary gear unit 33includes a sun gear 34 disposed for rotation in unison with the outputside of the fourth clutch 36, a pinion carrier 35 disposed for rotationin unison with the input side of the fourth clutch 36, and an internalgear 39 disposed for rotation in unison with the driven gear 31. The sungear 34 and the pinion carrier 35 are coupled together when the fourthclutch 36 is engaged.

Further, the subsidiary transmission mechanism 30 includes a third brake37 mounted on the casing 20 of the transmission 4 for fixing the sungear 34, and a one-way clutch (O/W clutch) 38 mounted on the casing 20in parallel, in respect of engine torque transmission, with the thirdbrake 37. The one-way clutch 38 locks the sun gear 34 to preventrotation of the sun gear 34.in the driving direction when the engagementof the fourth clutch 36 is released to release the engagement betweenthe sun gear 34 and the pinion carrier 35.

Then, rotation of the driven gear 31 caused by rotation of the inputshaft 11 of the main transmission mechanism 10 is transmitted to thecounter shaft 32 via the third planetary gear unit 33 and is furthertransmitted from the counter shaft 32 to a differential carrier 40.

In the automatic transmission 2 of this embodiment, as indicated inTable 1, a desired one of a plurality of shift positions including thefirst to fifth shift positions is established by controlling theengagement/disengagement of the first to fourth clutches 15, 17, 19, 36and the first to third brakes 22, 23, 37, which are friction engagingelements. In Table 1, a mark ◯ indicates the engaged state of eachclutch or brake and a mark Δ indicates the locked state of the one-wayclutch 38.

As indicated in Table 1, in order to establish a desired shift positionin the automatic transmission 2, the friction engaging elementsassociated with the desired shift position are engaged, so thatcorresponding ones of those shift change elements which contribute tothe power transmission in the shift position to be established areengaged.

For example, in order to establish the fifth shift position, the secondclutch 17, second brake 23 and fourth clutch 36 which are the frictionelements associated with the fifth shift position are engaged. By theengagement of the second clutch 17, the input shaft 11 and the pinioncarrier 16 which serve as a pair of shift change elements associatedwith the fifth shift position are engaged. Further, by the engagement ofthe second brake 23, the sun gear 18 and the casing 20 which serve as adifferent pair of shift change elements are engaged, and by theengagement of the fourth clutch 36, the sun gear 34 and the pinioncarrier 35 which serve as a still different pair of shift changeelements are engaged.

                  TABLE 1    ______________________________________                Shift Position    Friction engaging elements                  1st   2nd    3rd 4th 5th R   N, P 4'th    ______________________________________    Main    1st clutch 15                      ∘                            ∘                                 ∘                                     ∘    transmission            2nd clutch           ∘                                     ∘                                         ∘                                                      ∘    mechanism            17            3rd clutch 19                    ∘            1st brake 22                      ∘          ∘                                                 ∘            2nd brake 23    ∘                                         ∘                                                      ∘    Subsidiary            4th clutch 36            ∘                                         ∘    transmission            3rd brake 37                      ∘                            ∘                                 ∘                                             ∘                                                 ∘                                                      ∘    mechanism            O/W clutch                      Δ                            Δ                                 Δ              Δ            38    ______________________________________

In order to establish the third shift position, the first clutch 15, thesecond clutch 17 and the third brake 37 are engaged. In this embodiment,for the down-shift from the fifth shift position to the third shiftposition, that shift position (hereinafter referred to as 4'th shiftposition) which is not used in a normal shifting operation, that is, ina down-shift of one step or up-shift of one step, is used in the processof the down-shift. To establish the 4'th shift position, the secondclutch 17, second brake 23 and third brake 37 are engaged.

Therefore, in the down-shift from the fifth shift position to the 4'thshift position, the fourth clutch 36 is released and the third brake 37is engaged. Since an increase in the speed of the sun gear 34 can beprevented by the one-way clutch 38 even if the engagement of the thirdbrake 37 is not completed, there is no possibility that the sun gear 38is driven at an over speed even at the time of power-ON, i.e., at thetime of step-on of the accelerator pedal, so that the 4'th shiftposition is established.

Further, in the down-shift from the 4'th shift position to the thirdshift position, the second brake 23 is released and the first clutch 15is engaged. Thus, in the skip down-shift from the fifth shift positionto the third shift position, the function of the one-way clutch 38 canbe utilized by using the, 4'th shift position which is not used in thenormal shifting operation, as distinct from the conventional skipdown-shift from the fifth shift position to the third shift position byway of the fourth shift position, in which the function of the clutch 38is not utilized.

Next, the shift control process executed by the ECU 6 at the time of 5-3down-shift is explained with reference to the flowcharts of FIGS. 3 to 6and the graphs of FIGS. 7 to 12.

The graph of FIG. 7 shows a change in the turbine rotation speed N_(T)at the time of shift-down from the fifth shift position to the thirdshift position, with the elapse of time represented along the abscissa.

In relation to the shift control operation, the ECU 6 serving as shiftcommanding means periodically determines whether or not the throttlevalve opening degree θ traverses the shift line by use of the shift mapof FIG. 13 and on the basis of the output of the throttle sensor 9, inthe optimum shift position determining routine which is not shown.

When the driver steps on the accelerator pedal while the car is runningin the fifth shift position and if it is determined in the optimum shiftposition determining routine that the throttle valve opening degree θ ischanged from the point A to the point C in FIG. 13 and traverses the 4-3shift line, a 5-3 shift command is output and the 5-3 shift controlsubroutine of FIG. 3 is started (at the time point ss in FIGS. 7 to 11).This subroutine is executed at a predetermined control interval (forexample, 5 ms).

In the subroutine of FIG. 3, the ECU serving as subsidiary transmissionmechanism shift control means executes the 5-4' shift control subroutine(FIG. 4) in step 101.

As shown in FIG. 4, in the 5-4' shift control subroutine, thereleasing-side control subroutine for releasing the fourth clutch 36 ofthe subsidiary transmission mechanism 30 is first executed in step S111,the fourth clutch 36 serving as that friction engaging element whichcorresponds to the releasing-side shift change element in the 5-4'shifting process (releasing-side shift change element on thefifth-shift-position side). More specifically, the duty ratio of theelectromagnetic valve associated with supply/discharge of operating oilfor the fourth clutch 36 is controlled, as indicated by the solid linein FIG. 8, so as to discharge the operating oil from the fourth clutch36.

In the next step S112, the engaging-side control subroutine for engagingthe third brake 37 is executed. The third brake serves as that frictionengaging element which corresponds to the engaging-side shift changeelement in the 5-4' shifting process (engaging-side shift change elementon the 4'th shift position side). More specifically, the duty ratio ofthe electromagnetic valve associated with supply/discharge of operatingoil for the third brake 37 is controlled, so as to supply the operatingoil to the third brake 37.

In step S113, a preceding control subroutine (FIG. 5) for starting thereleasing control for the second brake 23 is executed prior to theestablishment of the 4'th shift position, the brake 23 being thefriction engaging element corresponding to the releasing-side shiftchange element in the 4'-3 shifting process (releasing-side shift changeelement on the 4'th shift position side).

In this preceding control subroutine, in step S121, the ECU 6 reads theoutput of the N_(E) sensor, which represents the engine rotation speedN_(E), and the output of the N_(O) sensor, which represents the rotationspeed N_(O) of the transmission output shaft, and determines the presentgear ratio. As the present gear ratio, an optimum shift positiondetermined in the optimum shift position determining routine describedbefore in relation to the 5-3 down-shift command is used, for example.Then, the torque converter speed ratio e is calculated based on theengine rotation speed N_(E), transmission output shaft rotation speedN_(O) and present gear ratio. The turbine torque T_(TM) corresponding tothe thus calculated speed ratio e is derived by referring to a speedratio e-turbine torque T_(TM) map (not shown) previously stored in theassociated memory device of the ECU 6. Further, a predetermined timeperiod t_(a) corresponding to the turbine torque T_(TM) is derived byreferring to a turbine torque T_(TM) --time period t_(a) map shown, byway of example, in FIG. 12, and whether or not the predetermined timeperiod t_(a) has elapsed from the time when the 5-3 shift command isoutput (point ss) is determined.

If it is determined in step S121 that the predetermined time periodt_(a) has not yet elapsed, and hence the result of the determination instep S121 is "NO", the electromagnetic valve, associated with supply ordischarge of operating oil with respect to the second brake 23 which isthe friction engaging element corresponding to the releasing-side shiftchange element on the 4'th shift position side, is driven with the dutyratio 0% in step S122. As a result, as indicated by the two-dot chainline in FIG. 11, the engaging hydraulic pressure for the second brake 23is rapidly reduced.

After the preceding control subroutine in the present cycle is completedas described above, the control flow proceeds to step S102 in FIG. 3,where the output of the N_(T) sensor 8 indicative of the present:turbine rotation speed N_(T) and the output of the N_(O) sensor 8aindicative of the rotation speed of the transmission output shaft areread, and the 4'th-shift-position in-gear rotation speed (the turbinerotation speed indicating that the 4'th shift position has beenestablished (4'th-shift-position synchronous rotation speed)) N_(TM) iscalculated by multiplying the output of the N_(O) sensor and the gearratio together. A 4'th-shift-position synchronization determiningthreshold value ΔN_(B) (for example, 40 rpm) previously stored in theassociated memory device of the ECU 6 is read therefrom, and a rotationspeed difference (N_(TM-) N_(T)) is calculated by deducting the presentturbine rotation speed N_(T) from the 4'th-shift-position in-gearrotation speed N_(TM). Further, if the rotation speed difference (N_(TM)-N_(T)) is equal to or less than threshold value ΔN_(B) is determined.

If the result of the determination in step 102 is "NO", execution of the5-3 shift control subroutine in the present cycle is completed, and thesame subroutine is started again when a control time interval haspassed. Therefore, the 5-4' shift control subroutine (step S101 in FIG.3 (steps S111 to S113 in FIG. 4)) is successively executed until theturbine rotation speed N_(T) becomes close to the 4'th-shift-positionin-gear rotation speed N_(TM).

Thus, as a result of the execution of 5-4' shift control subroutine(S101), the turbine rotation speed N_(T) is increased from thefifth-shift-position in-gear rotation speed (the turbine rotation speedindicating that the fifth shift position has been established(fifth-shift-position synchronous rotation speed)) N_(TI) to the4'th-shift-position in-gear rotation speed N_(TM).

Since the one-way clutch 38 is arranged in parallel to the third brake37, the one-way clutch 38 is locked at an appropriate time if the fourthclutch 36 is released simply with the duty ratio being 0% as shown inFIG. 8, so that the 4'th shift position is established and the shiftchange of the subsidiary transmission mechanism 30 is completed. Thatis, the engagement of the third brake 37 is performed at a proper time(when 4'th shift position synchronization is completed) after thelocking of the one-way clutch 38 as shown in FIG. 9.

During the time when the fifth shift position is established, since thefourth clutch 36 is engaged, the internal gear 39, carrier 35 and sungear 34 of the third planetary gear unit 33 rotate in unison in the samedirection at the same rotation speed.

However, the releasing of the fourth clutch 36 produces a difference inrotation speed among these elements.

In the 5-4' shift, since the engine 1 is in the power-ON state for whichthe accelerator pedal is stepped on, the speeds of the input shaft 11,drive gear 26 and driven gear 31 are increased. Accordingly, the speedof the internal gear 39 is also increased as compared with the time whenthe fifth shift position is established.

On the other hand, the carrier 35 is coupled to the load (tire) via thecounter shaft 32 and differential carrier 40. Therefore, during theshift, the carrier 35 rotates at the same rotation speed as thatobserved when the fifth shift position was established, that is, at arotation speed lower than that of the internal gear 39.

That is to say, the sun gear 34 is decreased in speed by being subjectedto a rotation force given by the internal gear 39 via the planetary gear35a and acting in the direction reverse to the rotation direction in theestablishment of the fifth shift position.

The speed of the sun gear 34 becomes zero at a certain point of time sothat the sun gear 34 is going to rotate in the reverse direction.However, the rotation is stopped by the locking of the one-way clutch38, and the 4'th shift position is achieved.

During the execution of the 5-4' shift control subroutine in asubsequent control cycle, if it is determined in the step S121 that thepredetermined time period t_(a) has elapsed from the time when the 5-3shift command is output, and therefore the result of determination inthe step S121 is "YES", the control flow proceeds to step S123, where itis determined whether or not the value of the flag F is "0" whichindicates that the predetermined time period t_(a) has just elapsed. Ifthe result of this determination is "YES", the value of the flag F isset to "1" (step S124), and the duty ratio D of the electromagneticvalve associated with the second brake 23 is set to the initial valueD_(H) (hereinafter referred to as initial duty ratio D_(H)) by the ECU6, which serves as engagement force reducing means (step S125). Next,the electromagnetic valve is driven with the duty ratio D set in step125 (step S126). Whereupon the execution of the preceding controlsubroutine in the present cycle is completed.

In the next cycle, the result of the determination in step S121 of thepreceding control subroutine becomes "YES", and the result of thedetermination in the step S123 becomes "NO". Therefore, the control flowproceeds to step S127, where the duty ratio D is set to a value (D_(H)-ΔD_(H)) which is obtained by deducting a predetermined value ΔD_(H)from the present initial duty ratio D_(H). Then, the electromagneticvalve is driven with the duty ratio D set in step S127 (step S126).Whereupon the execution of the control subroutine in the present cycleis completed.

In the subsequent cycles, a series of electromagnetic valve drivingprocesses consisting of steps S121, S123, S127 and S126 are executedrepeatedly. As a result, the duty ratio of the second brake 23, which isthe friction engaging element corresponding to the releasing-side shiftchange element on the 4'th shift position side, is gradually reducedfrom the initial duty ratio D_(H), which is set to a slightly largervalue by taking a margin for the sliding of the brake intoconsideration, as indicated by the solid line in FIG. 11. Therefore, theengaging hydraulic pressure for the second brake 23 is gradually loweredtoward the least sufficient hydraulic pressure as the 5-4' shift processproceeds, as indicated by the two-dot chain line in FIG. 11.

As described above, in the 5-4' shift process, the releasing control ofthe fourth clutch 36 (and the engaging control of the third brake 37) iscarried out, and the preceding control of the second brake which isreleased in the 4'-3 shift process is also carried out.

During the execution of the 5-3 shift control subroutine of FIG. 3, ifit is determined in step S102 that the condition that N_(TM) -N_(T)≦ΔN_(B) is satisfied, and therefore, if it is determined that the 4'thshift position has been established (point a in FIG. 11), then controlflow proceeds to the step 103, where a 4'-3 shift control subroutine isexecuted.

When N_(T) becomes substantially equal to N_(TM), the rotation of thesun gear 34 of the third planetary gear unit 33 in the drivingrotation-direction is locked by the one-way clutch 38 of the subsidiarytransmission mechanism 30, so that the one-way clutch 38 takes thedriving torque. Therefore, even when engagement of the third brake 37 isnot completed, the 4'th shift position is established.

As shown in FIG. 6, in the 4'-3 shift control subroutine, areleasing-side control subroutine for releasing the second brake 23 ofthe main transmission mechanism 10 is executed in the step S131(continuous execution from the step S113 of the 5-4' shift controlsubroutine), the second brake 23 being a friction engaging elementcorresponding to the releasing-side shift change element on the 4'thshift position side. That is, operating oil is gradually discharged fromthe second brake 23, so that the sun gear 18 of the second planetarygear unit 13 is gradually released. Also, in step S132, an engaging-sidecontrol subroutine for engaging the first clutch 15 is executed, thefirst clutch 15 being a friction engaging element corresponding to theengaging-side shift change element on the third shift position side.That is, operating oil is supplied to the first clutch 15, so that thesun gear 14 of the first planetary gear unit 12 is brought to be engagedwith the input shaft 11.

More specifically, in order to cause the changing rate of the turbinerotation speed N_(T) from the 4'th-shift-position in-gear rotation speedN_(TM) to the third-speed in-gear rotation speed N_(TJ) to be equal to atarget changing rate, the duty ratio of the electromagnetic valveassociated with the second brake 23 of the main transmission mechanism10 is feedback-controlled, as indicated by the solid line in FIG. 11,and the duty ratio of the electromagnetic valve associated with thefirst clutch 15 of the main transmission mechanism 10 is controlled asindicated by the solid line in FIG. 10. The feedback control (FBcontrol) is started when it is determined that the condition that N_(T)>N_(TM) +ΔN_(SB) is satisfied (FIG. 7), where the symbol ΔN_(SB) is adetermination threshold value (for example, 40 rpm). Switching of theduty ratio of the electromagnetic valve associated with the first clutch15 from 0% to 100% is effected at the time point a preset period beforethe time of determination of third-shift-position synchronization (timepoint c in FIGS. 7 to 10).

After this, as the 4'-3 shift process proceeds, the operating oil isdischarged from the second brake 23 to release the sun gear 18 of thesecond planetary gear unit 13, and the operating oil is supplied to thefirst clutch 15 to bring the sun gear 14 of the first planetary gearunit 12 to be coupled to the input shaft 11. As described above, theelectromagnetic valve associated with the first clutch 15 is driven withthe duty ratio 100% from the time before the time point of determinationof third-shift-position synchronization (time point c). For this reason,the ineffective stroke of the first clutch 15 is just finished at thetime of determination of third-shift-position synchronization, therebyrendering torque transmission via the first clutch 15 possible.

Even if the initial duty ratio DH employed in releasing the second brake23, as described above, is set to a value such that the slipping of thesecond brake 23 is reliably avoided in the 5-4' shift process and thesecond brake 23 begins to slip just when the 4'th shift position isestablished, the initial duty ratio D_(H) varies from transmission totransmission so that the initial duty ratio D_(H) is smaller than theoptimum value or inversely larger because the automatic transmission 2(friction elements and electromagnetic valves) has an operatingvariation due to a manufacture error, deterioration with elapse of time,etc.

When the initial duty ratio D_(H) is smaller than the optimum value, thesecond brake 23 begins to slip during the 5-4' shift process, so thatthe determination of completion of the 5-4' shift process(synchronization determination for 4'th shift position) cannot beconducted correctly, thereby making it impossible to carry out propershift control.

That is, despite the fact that the subsidiary transmission mechanism 30is actually in shift change, operation (during the 5-4' shift process),the rotation speed of the input shaft 11 detected by the, N_(T) sensor 8becomes a value equivalent to the rotation speed in the 4'-3 shiftprocess. Thus, it is mistakenly determined based on the improperlydetected rotation speed and the detection value from the N_(O) sensor 8athat the shift change in the subsidiary transmission mechanism 30 sidehas completed. In this case, the third brake 37 is engaged, so that theshift change on the subsidiary transmission mechanism 30 in the shiftprocess is forcibly finished, thereby producing a shock.

On the other hand, when the initial duty ratio D_(H) is larger than theoptimum value, the releasing operation of the second brake 23 delays, sothat the relation between the 5-4' shift and the 4'-3 shift is notcontinuous, and a temporal stoppage occurs at the 4'th shift position(two-dot chain line in FIG. 7). Therefore, since the start of the 4'-3shift process delays, the total shift time is consequently a increased,and a shock still occurs at the time when the 4'th shift position isestablished.

In this embodiment, therefore, the sum of a reference duty ratio D_(HO)previously stored in the ROM of the ECU 6 and a learned value D_(HLi) isused as the duty ratio D_(H) of the electromagnetic valve associatedwith the second brake 23, and the learned value D_(HLi) is subject to alearning-correction.

In this embodiment, paying attention to the fact that the average valueof the turbine rotation speed changing rate N_(T) (gradient of theturbine rotation speed N_(T)) is higher as shown in FIG. 14 when thehydraulic pressure supplied to the second brake .23 (initial duty ratioD_(H)) is too low, while it is lower as shown in FIG. 15 when thehydraulic pressure is too high, the initial duty ratio D_(H) islearning-corrected based on the average turbine rotation speed changingrate N_(TAVE) within a predetermined time (for example, 64 ms) from thecompletion of shift change in the subsidiary transmission mechanism 30(determination of completion of 5-4' shift process) so that the 5-4'shift and the 4-3 shift are connected smoothly.

The control process for learning correction of the initial duty ratioD_(H) will be described below.

In parallel to the shift routine shown in FIGS. 3 to 6, the learningcorrection routine shown in FIG. 17 is executed at predeterminedintervals by the ECU 6, which serves as learning correction means.

In this learning correction routine, it is first determined by theprocess in step S102 shown in FIG. 3 whether or not the 4'th shiftposition has been established (step S201). If the result of thisdetermination is "NO", the execution of the learning correction routinein the present control cycle is completed.

If it is concluded in the step S201 in a subsequent cycle of executingthe learning correction routine that the 4'th shift position has beenestablished, and therefore, the result of the determination in step S201is "YES", the control flow proceeds to step S202.

In step S202, a determination is made as to which of a plurality ofpredetermined turbine rotation speed regions, for example, regionsdivided into four as shown in Table 2, the turbine rotation speed N_(T)at the start time of 5-4' shift belongs. According to the result of thedetermination, one of first to fourth learning RAMs corresponding to thefirst to fourth turbine rotation speed regions, respectively, isselected. The initial duty ratio learned values D_(HLi) (i=1 to 4) arestored in the first to fourth learning RAMs, respectively, in a mannerpermitted to be updated. The learned value D_(HLi) is read from theselected RAM, and stored in an associated one register of the ECU 6.

                  TABLE 2    ______________________________________                  Turbine rotation speed NT (rpm)    ______________________________________    1st turbine rotation speed region                    NT < 2000    2nd turbine rotation speed region                    2000 ≦ NT < 2600    3rd turbine rotation speed region                    2600 ≦ NT < 3200    4th turbine rotation speed region                    3200 ≦ NT    ______________________________________

The reason why the learning correction of the duty ratio D_(H) is madefor each turbine rotation speed region based on the turbine rotationspeed N_(T) at the start time of 5-4' shift as described above is thatthe hydraulic pressure supplied to the second brake 23 is intended to becontrolled finely according to the vehicle operating condition at thestart time of shifting.

In the next step S203, the average value N_(TAVE) of turbine rotationspeed changing rates is determined. Therefore, an average turbinerotation speed change rate calculating subroutine shown in FIG. 18 isexecuted at predetermined intervals (for example, 16 ms).

In this subroutine, it is first determined whether or not the value ofthe flag F is "1" which indicates that the average turbine rotationspeed changing rate N_(TAVE) is being calculated (step S211). If theresult of this determination is "NO", the output of the N_(T) sensor 8,which represents the turbine rotation speed N_(T), is read and stored inthe RAM (step S212). Next, the counter value I representing the numberof calculations of the average turbine rotation speed changing rateN_(TAVE) and the sum SUM of the turbine rotation speed changing ratesN_(T) are reset to "0" (steps S213 and S214). Further, the value of theflag F is set to "1" (step S215), and the subroutine in the presentcycle is completed.

In the next subroutine execution cycle, the result of the determinationin step S211 is "YES", and the control flow proceeds to step S216, whereit is determined whether or not the counter value I is equal to "4",that is, whether or not a predetermined time Δ Telapses from the timewhen 4'th shift position is established. In the second subroutineexecution cycle, the result of the determination in step S216 is "NO",and the output of the N_(T) sensor is read and stored in the RAM (stepS217). Next, by the ECU 6, which serves as counting means, the countervalue is increased by "1" (step S218).

In the next step S219, the turbine rotation speed changing rate N_(T) iscalculated based on the turbine rotation speed N_(T) detected in stepS212 in the preceding cycle, the turbine rotation speed N_(T) detectedin the step S217 in the present cycle, and the subroutine executionperiod. The calculated turbine rotation speed changing rate N_(T) isadded to the present total sum SUM of the turbine rotation speedchanging rates. Next, it is again determined whether or not the countervalue I is equal to "4" (step S220). If the result of this determinationis "NO", the execution of the subroutine in the present cycle iscompleted.

In the next subroutine execution cycle, the control flow proceeds to thestep S219 through steps S211, S216 and S218, where the sum SUM of theturbine rotation speed changing rates is updated.

Subsequently, the sum SUM of the turbine rotation speed changing ratesis updated in the same way. If it is concluded in the next step S220that the count value I is equal to "4", the ECU 6, which serves asaverage value calculating means, calculates the average turbine rotationspeed changing rate N_(TAVE) by dividing the sum SUM by a value "4"(step S221), and writes the calculated value N_(TAVE) in the RAM (stepS222). Whereupon, the execution of the subroutine in the present cycleis completed.

In the next subroutine execution cycle, the control flow proceeds tostep S216 through step S211, where it is concluded that the count valueI is equal to "4". Then, the control flow proceeds to step S223, wherethe flag F is reset to "0". Thus, the execution of this subroutine iscompleted, and the control flow proceeds to step S204 of the mainroutine shown in FIG. 17.

In step S204, a determination is made as to whether or not the averageturbine rotation speed changing rate N_(TAVE) is equal to or greaterthan the target upper limit value N_(TA). If the result of thisdetermination is "NO", the control flow proceeds to step S205, where itis further determined whether or not the average turbine rotation speedchanging rate N_(TAVE) is equal to or smaller than the target lowerlimit value N_(TB). If the result of the determination in the step S205is "NO", it is judged that the value of the initial duty ratio D_(H),set at the present, is between the target upper limit value N_(TA) andthe target lower limit value N_(TB), and therefore, that the hydraulicpressure supplied to the second brake 23 is within a proper range.Thereupon, the learning correction subroutine shown in FIG. 17 iscompleted without making the learning correction of the initial dutyratio D_(H).

On the other hand, if it is concluded in step S204 that the averageturbine rotation speed changing rate N_(TAVE) is equal to or greaterthan the target upper limit value N_(TA), it is judged that the initialduty ratio D_(H) is too small. In this case, the control flow proceedsto the step S206, where a learning correction amount ΔD_(HL) (forexample, 1.2%) is added to the learned value D_(HLi) set at the present.Next, the learned value D_(HLi) thus increased is stored in the RAM(step S207). Whereupon, the learning correction routine shown in FIG. 17is completed.

Inversely, if it is concluded in the step S205 that the average turbinerotation speed changing rate N_(TAVE) is equal to or smaller than thetarget lower limit value N_(TB), it is judged that the initial dutyratio D_(H) is too large. In this case, the control flow proceeds to thestep S208, where a learning correction amount ΔD_(HL) is deducted fromthe learned value D_(HLi) set at the present. Next, the learned valueD_(HLi) thus decreased is stored in the RAM (step S207). Whereupon, thelearning correction routine shown in FIG. 17 is completed.

This learned value D_(HLi) is added to a reference initial duty ratioD_(HO), which has been set beforehand in the ECU 6, and the resultantvalue is used as the initial duty ratio D_(H) in the next 5-3 shiftprocess.

When the learning correction of the initial duty ratio D_(H) is madeeach time 5-3 shift is carried out as described above, the averageturbine rotation speed changing rate N_(TAVE) converges to a valuebetween the target upper limit value N_(TA) and the target lower limitvalue N_(TB), and the initial duty ratio D_(H) is made proper.Thereupon, even when variations in manufacture or deterioration withelapse of time occurs on the automatic transmission 2, a smooth 5-3shift is carried out. In this case, as shown in FIG. 16, the turbinerotation speed N_(T) increases continuously with a proper averageturbine rotation speed changing ratio.

The shift control apparatus according to the present invention is notlimited to the above embodiment, and various modifications can be made.

For example, in the above embodiment, this invention is applied to adown-shift from the fifth shift position to the third shift position,but this invention can be applied to other skip down-shift, for example,from the fourth shift position to the second shift position or from thesixth shift position to the fourth shift position depending on thestructure of the automatic transmission 2.

Also, in this embodiment, the learned value D_(HLi) of the duty ratio isset for each turbine rotation speed region, but the duty ratio learnedvalue D_(HLi) can be set for each turbine torque region. In this case,for example, by the ECU 6, which serves as input shaft torque detectingmeans, the torque converter speed ratio e is calculated from the enginerotation speed N_(E), transmission output shaft rotation speed N_(O),and the present gear ratio as with the case explained relating to thestep S121 in FIG. 5, and further the turbine torque is determined fromthe calculated torque converter speed ratio e.

We claim:
 1. A shift control method for an automotive automatictransmission having a first transmission mechanism connected to an inputshaft of the automatic transmission and a second transmission mechanismconnected to the first transmission mechanism in series with respect tothe first transmission mechanism in a power transmission system, each ofsaid first and second transmission mechanisms being constructed toselectively establish plural gear positions, and said automatictransmission being constructed to selectively establish first and secondshift positions by a combination of a gear position established in thefirst transmission mechanism and a gear position established in thesecond transmission mechanism, comprising:starting a shift changeoperation for establishing a gear position, corresponding to the secondshift position, in the second transmission mechanism in response to ashift command instructing a shift from the first shift position to thesecond shift position; starting a shift change operation forestablishing a gear position, corresponding to the second shiftposition, in the first transmission mechanism before the shift changeoperation in the second transmission mechanism is completed; detecting arotation speed of the input shaft of the automatic transmission; andlearning-correcting a value of a parameter governing start of shiftchange in the first transmission mechanism based on rotation speedinformation, wherein said rotation speed information consists of achanging rate of the detected input shaft rotation.
 2. A shift controlmethod for an automotive automatic transmission according to claim 1,wherein said step of learning-correcting the value of the parameterincludes learning-correcting the value of the parameter based on achanging rate of the rotation speed of the input shaft observed during atime period from a time the shift change operation in the secondtransmission mechanism is completed to a time a predetermined period oftime has elapsed since start of the shift change operation in the firsttransmission mechanism.
 3. A shift control method for an automotiveautomatic transmission according to claim 1, wherein the parameter is anengagement force of a friction element in the first transmissionmechanism which is released when establishing the second shift position,andsaid step of starting the shift change operation in the firsttransmission mechanism includes decreasing the engagement force of thefriction element.
 4. A shift control method for an automotive automatictransmission according to claim 3, wherein said step of starting theshift change operation in the first transmission mechanism includesdecreasing the engagement force of the friction element to a presetvalue, andsaid step of learning-correcting the value of the parameterincludes learning-correcting said preset value based on the changingrate of the detected rotation speed of the input shaft.
 5. A shiftcontrol method for an automotive automatic transmission according toclaim 1, wherein a speed ratio of the first shift position is smallerthan a speed ratio of the second shift position.
 6. A shift controlmethod for an automotive automatic transmission according to claim 5,wherein said automatic transmission is constructed to selectivelyestablish a third shift position, a speed ratio of the third shiftposition being greater that the first shift position and smaller thanthe second shift position.
 7. A shift control method for an automotiveautomatic transmission having a main transmission mechanism and asubsidiary transmission mechanism which are arranged in series with eachother in a power transmission system and each of which is constructed toselectively establish plural gear positions, said automatic transmissionbeing constructed to selectively establish the first and second shiftpositions by a combination of a gear position established in the maintransmission mechanism and a gear position established in the subsidiarytransmission mechanism, comprising:starting a shift change operation forestablishing a gear position, corresponding to the second shiftposition, in either one of the main and subsidiary transmissionmechanisms in response to a shift command instructing a shift from thefirst shift position to the second shift position; starting a shiftchange operation for establishing a gear position, corresponding to thesecond shift position, in the other transmission mechanism before theshift change operation in said one of the transmission mechanisms iscompleted; detecting an input shaft rotation speed of the automatictransmission; and learning-correcting a value of a parameter governingstart of shift change in said other transmission mechanism based on achanging rate of the input shaft rotation speed, wherein said step oflearning-correcting the value of the parameter includes the step ofdetermining an average value of changing rates of the input shaftrotation speed and learning-correcting the value of the parameter basedon the determined average value.
 8. A shift control method for anautomotive automatic transmission having a main transmission mechanismand a subsidiary transmission mechanism which are arranged in serieswith each other in a power transmission system and each of which isconstructed to selectively establish plural gear positions, saidautomatic transmission being constructed to selectively establish thefirst and second shift positions by a combination of a gear positionestablished in the main transmission mechanism and a gear positionestablished in the subsidiary transmission mechanism,comprising:starting a shift change operation for establishing a gearposition, corresponding to the second shift position, in either one ofthe main and subsidiary transmission mechanisms in response to a shiftcommand instructing a shift from the first shift position to the secondshift position; starting a shift change operation for establishing agear position, corresponding to the second shift position, in the othertransmission mechanism before the shift change operation in said one ofthe transmission mechanisms is completed; detecting an input shaftrotation speed of the automatic transmission; detecting torque of theinput shaft; and learning-correcting a value of a parameter governingstart of shift change in said other transmission mechanism based on achanging rate of the input shaft rotation speed, wherein said step oflearning-correcting the value of the parameter includeslearning-correcting the value of the parameter for each of those regionswhich are divided in accordance with the detected input shaft rotationspeed or the detected torque of the input shaft.
 9. A shift controlmethod for an automotive automatic transmission according to claim 8,wherein said torque detecting step includes the step of detecting saidtorque of the input shaft based on a torque converter speed ratio.